#include <stdio.h>

int main(int argc, char const *argv[])
{
    char ch;
    printf("in a char:");
    ch = getchar();

    if (ch >= 'a' && ch <= 'z') {
        ch = ch - ('a' - 'A');
        // ch = ch + 32;
    } else if (ch >= 'A' && ch <= 'Z') {
        ch = ch - ('A' - 'a');
        // ch = ch - 32;
    }

    printf("ch = %c \n", ch);

    return 0;
}